How do I fix the GPG error "NO_PUBKEY" on Ubuntu

GPG error NO_PUBKEY

You have seen error like this below when adding a new repository on Ubuntu Software & Updates -> Other software?

GPG error: http://ppa.launchpad.net trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 409C8B51283EC8CD

Don't worry? I  will share two solution how to tackle it. Here they are :

1. The quick way is by running command on terminal. Execute the following commands in terminal (replace key with the key on error message after NO_PUBKEY ): 

                      sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 409C8B51283EC8CD

              and then update 

                           sudo apt-get update

     2.   Using grapical application i.e. Y-PPA-Manager          

1.  To install it, first add the webupd8 repository for this program:
         sudo add-apt-repository ppa:webupd8team/y-ppa-manager
2.  Update your software list and install Y-PPA-Manager:
         sudo apt-get update
         sudo apt-get install y-ppa-manager
3.  Run y-ppa-manager.
     When the main y-ppa-manager window appears, click on "Advanced."
     From the list of advanced tasks, select "Try to import all missing GPG keys" and click      OK.

I hope you enjoy your journey on Ubuntu. Cheers ^_^